Permanent magnet system for travelling wave tubes

ABSTRACT

Permanent magnet beam-focusing apparatus comprises a plurality of permanent magnets having pole shoes arranged in a stacked relationship and secured in a plurality of interlocked comblike metal sheets of quadrilateral cross section, the pole shoes resiliently abutting individual fitting edges of the comb teeth to accurately position the magnetic field established by the permanent magnets.

United States Patent l lnvcmof Sand [50] Field of Search 335/210; Munich, Germany 315/35, 5.35 [2| Appl. No. 4,541 [22] Filed Jan. 2|, I970 References Cited palfimed fl UNITED STATES PATENTS 1731 'z a 3,241,007 3/1966 Eder 335 210 3289 031 11 1966 11' ts t 1 315 3.5 Priority J 28,1969 1rama ue a 3 31 Gummy Primary ExaminerG. Harris [3] P 19 ()4 131,7 AttorneyHill, Sherman, Meroni, Gross & Simpson ABSTRACT: Permanent magnet beam-focusing apparatus [54] EM FOR comprises a plurality of permanent magnets having pole shoes 1 0 Claim 4 D in arranged in a stacked relationship and secured in a plurality of g interlocked comblike metal sheets of quadrilateral cross sec- [52] US. Cl 335/210, tion, the pole shoes resiliently abutting individual fitting edges 315/535 of the comb teeth to accurately position the magnetic field [5 l Int. Cl H0" 7/00 established by the permanent magnets.

PATENTEUSEP H97! 3503 90 Fug] INVENTOR ATTYS.

PERMANENT MAGNET SYSTEM FOR TRAVELLING WAVE TUBES BACKGROUND OF THE INVENTION I. Field of the Invention The instant invention relates to a permanent magnetic system for the focused guidance of at least one electron beam over a relatively great distance, more particularly for travelling wave tubes, wherein the permanent magnets are disposed axially symmetrically to the electron beam and wherein there are disposed one behind the other in the direction of the electron beam alternately crossing pole shoes which, provided with a bore for receiving the discharge vessel, extend transversely of the direction of the electron beam, whereby the pole shoes having even ordinal numbers are connected with like poles of a polarity of the permanent magnets, and the pole shoes having odd ordinal numbers are connected with like poles of the other polarity of the permanent magnets, so that along the length of the electron beam axis there is provided a magnetic field alternating in direction and having a substantially sinusoidal magnetic field strength characteristic.

2. Description of the Prior Art This type of permanent magnetic system is old in the art (compare German Pat. No. 1,076,280). The manufacture of such a permanent magnetic system is comparatively complicated and expensive due to the great production accuracy required. With a stack construction in accordance with the arrangement of the aforementioned patent the individual tolerances of the pole shoes and intermediate rings stacked one above the other are additive. In the generally elongated magnetic systems containing a very great number of pole shoes, this has as a consequence that the maxima, minima and zero passages of the magnetic field after a certain distance are removed so far from their ideal positions that a tube placed in such a magnetic field can no longer be operated rationally.

However, the fabrication of the pole shoes and intermediate rings required for the stack construction with such a small tolerance that even in an elongated construction such a danger is ruled out, would lead to prohibitively high costs in addition to the considerable manufacturing difficulties connected therewith.

The problem of a true-to-size construction of this type of permanent magnetic systems is of particular importance for the increasingly important case of integrated travelling wave tubes, wherein the entire tube arrangement inclusive the magnetic system surrounding it is discarded upon breakdown of any part of the tube. To realize this type of integrated tube at a justifiable technical and financial expense, a simple true-tosize construction of the permanent magnetic system is of decisive importance.

SUMMARY OF THE INVENTION To solve this problem the invention proposes in a permanent magnetic system of the type mentioned initially that the pole shoes be combined into a self-supporting pole shoe system, wherein four comblike metal sheets are provided which by means of straps formed thereon are inserted into one another to interconnect the sheets to form a frame having a quadrilateral cross section and having teeth provided on each side with fitting edges, on which edges pole shoes are interposed between the teeth and abut resiliently.

As a result of this step, wherein the fixing of the position of the individual pole shoes only occur: through the fitting edges of the comblike metal sheets, deviations of the individual-pole shoes from their ideal strengths can have no influence whatever on the magnetic field. The comblike metalsheets may simply be fabricatedby punching or milling through a programmed automatic machine having adequate fitting accura- The comblike metal sheets may form a leg of a sheet metal part curved in the shape of a Z so that the other legs of this sheet metal part after the putting together into the pole shoe frame may serve a simple grouping of the permanent magnets about the pole shoe system.

For the functioning of a permanent magnetic system in ac cordance with the invention it is only important that the pole shoe bear closely against the fitting edges of the comblike metal sheets. To accomplish such a snug fit which serves at the same time for retaining the pole shoe, the invention provides in a further development that in the intermediate spaces between two successive teeth there is formed on the sheet metal a tongue which extends in substantially parallel relation to the fitting edge, such that the smallest distance thereof from the fitting edge is smaller than the thickness of the pole shoe interposed between it and the fitting edge. This is simply accomplished in that the tongues which normally have a slightly greater distance than the thickness of the pole shoe have a projection in the area of its free ends directed to the fitting edge. The accurate position of the projection directed to the fitting edge is obtained, depending on the type and thickness of the sheet as well as the width of the tongues, by the pressure of the pole shoes against the fitting edges required for a snug fit and effective retention.

To achieve an effective magnetic termination of the pole shoes to the permanent magnets grouped thereabout along the surfaces of the frame, the invention provides in a further development that the parts of the pole shoes projecting outwardly through the comblike metal sheets have a larger cross section than the parts of the pole shoes disposed in the proximity of the electron beam. To avoid a loss of magnetic flux due to the gaps existing between the pole shoes, all poles shoes projecting outwardly through a comblike metal sheet are bridget by a common soft iron plate on which permanent magnets are placed.

In order to provide for ease in assembly of the comblike metal sheets into a frame, the invention provides in a further development that the straps are so formed and disposed that they project outwardly through a notch between two teeth of the opposite metal sheet. The comblike metal sheets are then simply fixed by bending the straps back. Should the relatively great stability of the frame achieved thereby not be sufficient for special purposes, the metal sheets can be glued with an adhesive, e.g. araldite, or soldered with one another.

As as result of the combination of the pole shoes of the permanent magnetic systems into a self-supporting pole shoe system, there exists at the same time the possibility of using this pole shoe system as supporting body for the input and output hollow waveguides which supply the high frequency energy to a tube inserted into the axial bore of the pole shoe system or to receive high frequency energy therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described with reference to a preferred embodiment which is illustrated in the accompanying drawings, wherein for the sake of clarity the permanent magnets have been left out. In the drawings, like parts are provided with like reference characters.

FIG. 1 is a side view of a pole shoe system of a permanent magnetic system according to the invention provided with an input and output hollow waveguide;

FIG. 2 is a top view of an arrangement according to FIG. 1 along the line II-II without input or output hollow waveguides;

FIG. 3 is a cross-sectional view along the line III-III of the arrangement shown in FIG. 2; and

FIG. 4 is a side view of the combined pole shoes without the comblike metal sheets.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS The pole shoe system according to the invention shown in FIG. 1 may have any-desired length which may go far beyond the twelve pole shoes shown as indicated by the illustration being broken through in the middle. Of the four sheet metal parts 1, 2, 3 and 4 visible in FIG. 2, whose legs 11, 12, 13 and 14 are slitted as comblike metal sheets, shown in FIG. 3, the metal sheet parts 2 and 3 are visible in FIG. 1. Each of the comblike metal sheets 11 to 14 is Z-shaped and includes individual teeth, e.g. 112, between which lie notches formed by punching or milling, of which only the notches 212 formed in the comblike metal sheet part 12 are visible in the drawings. In each case, the edges 312 of the comblike metal sheet 12 and, therefore, also of the remaining metal sheets 11, 13 and 14 are formed as fitting edges, which have a constant measured distance relative to each other, in addition to a most accurate parallel relationship. Pole shoes 30 and 31 bear against these fitting edges so that the deviations of the pole shoe thickness in their thinner inner section 130 and 131 caused by the manufacturing tolerances can have no influence on the course of the magnetic field.

To fix the pole shoes in their positions on the fitting edges 312 (or the corresponding fitting edges of the other comblike metal sheets) tongues 215 are formed in the notches 212 which, extending parallel to the fitting edges, 312, have a slightly larger distance along the greater part of their lengths from the fitting edges than the thickness of the middle sections 130 and 131 of the pole shoes. Adjacent their free ends these tongues 215 have thick portions 216 which form projections particularly directed toward the fitting edge and protruding from the general course of the tongue.

The thickened portions 216 the pole shoes are pressed, upon insertion, between the tongues 215 and the fitting edges 312 against the latter, so that owing to the exact distance of the fitting edges which may be simply established, an accurate pole division is assured.

The teeth of the comblike metal sheets 11 to 14 are provided with projecting straps 411 to 414, whereby the metal sheet portions are so slotted or so staggered that the teeth of opposite comblike metal sheets are staggered parallel behind one another and by one half tooth frequency with respect to the teeth of the two comblike metal sheets directed perpendicularly thereto. Through this step it is possible by simple means to assemble the individual metal sheets together, such that in each case the straps 411 to 414 of a comblike metal sheet can be inserted through the notch between a tongue and a fitting edge of the metal sheet disposed perpendicularly thereto. For this purpose, it is of course necessary that the extension of the pole shoes directed parallel to the fitting edges be smaller, by at least the thickness of the metal sheets, than the depth of the notches between the individual teeth, so that it is possible that the teeth between the lower edge of the notches 212 and the opposite edge of the pole shoes 31 receive the straps. By bending back the straps 411 to 414, the metal sheets 1 to 4 so assembled are combined into a fixed frame, whereby as an additional safeguard the metal sheets may be glued or soldered.

As evident from FIG. 1, a pole shoe system according to the invention can at the same time serve as supporting body for the input and output hollow waveguides 20 and 21. For this purpose, in the preferred embodiment shown pins 22 to 25 are provided in the input and output hollow waveguides which come to lie in a comer of a Z-shaped metal sheet part 1 to 4 and are glued or soldered therewith.

in FIG. 4, wherein the arrangement of the built-in pole shoes is illustrated, the comblike metal sheets for fixing the positions of the pole shoes relative to each other have been omitted to afford a better view. In the openings 27 of the individual pole shoes 30 and 31 which are aligned one behind the other, there is inserted a so-called field straightener 28 particularly as a means for avoiding azimuthal dissymmetries, for homogenizing the magnetic field, said field straightener being composed in a manner known per se alternately of magnetic and nonmagnetic rings.

The outer surfaces of the pole shoes 30 and 31 facing each other are bridged by a soft iron rail so that when permanent magnets are placed on said soft iron rail, a loss of magnetic flux due to interspaces between the individual pole shoes is avoided. Permanent magnets are then placed on said soft iron rails, such that the permanent magnets being in communication with the pole shoes 30 bear with their south poles and the permanent magnets being in communication with the pole shoes 31 bear with their north poles against the soft iron rails, or vice versa.

This construction has been partially shown in FIG. 2 wherein the pole shoes 30 are bridged by a soft iron rail 416 and the pole shoes 31 are bridged by a soft iron rail 415. The north and south poles, respectively, of a plurality of permanent magnets, here referenced with 417 and 418, abut the rails 415 and 416.

In accordance with the arrangement of the German Pat. No. 1,076,280, the poles of the permanent magnets remote from the soft iron rails and, therefore, remote from the pole shoes 30 and 31, are advantageously short circuited by soft-magnetic rails. Since, moreover, the grouping of such permanent magnets about the pole shoes is, for example, sufficiently dis closed in the aforementioned German Pat. No. 1,076,280, these permanent magnets have been partially shown in the drawings.

A simply and inexpensively fabricated extremely true-to size magnetic system is provided by the invention, a permanent magnetic system containing a self-supporting pole shoe system which may serve not only as supporting body for the input and output hollow waveguides but at the same time also for the tube to be inserted in the bore 27.

The invention is not limited to the embodiment shown in the drawings. 1t is also possible, in addition to an arrangement of the projections 212 in another location of the tongue, to omit the tongues entirely and instead to interpose a suitable leaf spring between the edge of the following tooth facing a fitting edge and a pole shoe, said leaf spring being supported both on this edge and on the pole shoe. Likewise, it would also be possible to choose an arrangement, wherein the pole shoes 30 and 31 cross not vertically but at any other angle, whereby this angle is only limited by the requirement that the permanent magnets to be fixed on the outer surfaces of the pole shoes do not disturb each other.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

What 1 claim is:

1. A permanent magnetic system for the focused guidance of at least one electron beam over a comparatively large distance, more particularly for travelling wave tubes, wherein the permanent magnets are disposed axially symmetrically to the electron beam and wherein in the direction of the electron beam there are disposed one behind the other alternately crossing pole shoes which, provided with a bore for receiving the discharge vessel, extend transversely of the direction of the electron beam, whereby the pole shoes of even ordinal numbers are connected with like poles of a polarity of the permanent magnets, and the pole shoes having odd ordinal numbers are connected with like poles of the other polarity of the permanent magnets, so that along the length of the electron beam axis there arises a magnetic field alternating in direction and having a substantially sinusoidal run of the magnetic field strength, the improvement therewith that the pole shoes are combined into a self-supporting pole shoe system comprising a plurality of comblike members, each of said members having spaced-apart teeth, each tooth having a fitting edge and said teeth receiving said pole shoes therebetween with the individual pole shoes abutting the corresponding fitting edges, and each of said members having at least one projecting strap for extending between adjacent teeth of another such member for securing said members together.

2. A permanent magnetic system as defined in claim 1, wherein each of said comblike members form a leg of a Z- shaped metal sheet part.

3. A permanent magnetic system as defined in claim 1, characterized in that in the interspaces between two successive teeth there is formed a tongue extending substantially parallel to said fitting edge such that the smallest distance thereof from the fitting edge is smaller than the thickness of a pole shoe interposed between it and the fitting edge.

4. A permanent magnetic system as defined in claim 3, characterized in that the tongues in the area of their free ends each have a projection directed toward the fitting edge.

5. A permanent magnetic system as defined in claim I, wherein the parts of the pole shoes projecting outwardly through the comblike members have a larger cross section than the parts of the pole shoes disposed in the vicinity of the electron beam.

6. A permanent magnetic system as defined in claim I, wherein all pole shoes projecting outwardly through a comblike members are bridged by a common soft iron plate on which permanent magnets are placed.

7. A permanent magnetic system as defined in claim 1, wherein said straps are formed and disposed such that they project outwardly through a slot between two teeth of an adjacent one of said members and rearwardly from the tips of the teeth,

8. A permanent magnetic system as defined in claim 1, wherein the comblike members put together are fixed by bending the straps back against the other member.

9. A permanent magnetic system as defined in claim 1, wherein the pole shoe system comprises and is utilized as supporting body for, means for supplying high frequency energy to the discharge vessel from a hollow waveguide and means for coupling high frequency energy from the discharge tube to a hollow waveguide.

10. A permanent magnet system as defined in claim 1, wherein said comblike members are metallic and wherein four of said members are interconnected by said projecting members to form a structure having a quadrilateral cross section. 

1. A permanent magnetic system for the focused guidance of at least one electron beam over a comparatively large distance, more particularly for travelling wave tubes, wherein the permanent magnets are disposed axially symmetrically to the electron beam and wherein in the direction of the electron beam there are disposed one behind the other alternately crossing pole shoes which, provided with a bore for receiving the discharge vessel, extend transversely of the direction of the electron beam, whereby the pole shoes of even ordinal numbers are connected with like poles of a polarity of the permanent magnets, and the pole shoes having odd ordinal numbers are connected with like poles of the other polarity of thE permanent magnets, so that along the length of the electron beam axis there arises a magnetic field alternating in direction and having a substantially sinusoidal run of the magnetic field strength, the improvement therewith that the pole shoes are combined into a self-supporting pole shoe system comprising a plurality of comblike members, each of said members having spaced-apart teeth, each tooth having a fitting edge and said teeth receiving said pole shoes therebetween with the individual pole shoes abutting the corresponding fitting edges, and each of said members having at least one projecting strap for extending between adjacent teeth of another such member for securing said members together.
 2. A permanent magnetic system as defined in claim 1, wherein each of said comblike members form a leg of a Z-shaped metal sheet part.
 3. A permanent magnetic system as defined in claim 1, characterized in that in the interspaces between two successive teeth there is formed a tongue extending substantially parallel to said fitting edge such that the smallest distance thereof from the fitting edge is smaller than the thickness of a pole shoe interposed between it and the fitting edge.
 4. A permanent magnetic system as defined in claim 3, characterized in that the tongues in the area of their free ends each have a projection directed toward the fitting edge.
 5. A permanent magnetic system as defined in claim 1, wherein the parts of the pole shoes projecting outwardly through the comblike members have a larger cross section than the parts of the pole shoes disposed in the vicinity of the electron beam.
 6. A permanent magnetic system as defined in claim 1, wherein all pole shoes projecting outwardly through a comblike members are bridged by a common soft iron plate on which permanent magnets are placed.
 7. A permanent magnetic system as defined in claim 1, wherein said straps are formed and disposed such that they project outwardly through a slot between two teeth of an adjacent one of said members and rearwardly from the tips of the teeth.
 8. A permanent magnetic system as defined in claim 1, wherein the comblike members put together are fixed by bending the straps back against the other member.
 9. A permanent magnetic system as defined in claim 1, wherein the pole shoe system comprises and is utilized as supporting body for, means for supplying high frequency energy to the discharge vessel from a hollow waveguide and means for coupling high frequency energy from the discharge tube to a hollow waveguide.
 10. A permanent magnet system as defined in claim 1, wherein said comblike members are metallic and wherein four of said members are interconnected by said projecting members to form a structure having a quadrilateral cross section. 